Electron discharge device of the cavity resonator type



July 4, 1950 PlERCE 2,513,359

ELECTRON DISCHARGE DEVICE OF THE CAVITY RESONATOR TYPE Filed Feb. 1, 1945 7 2 Sheets-Sheet l ONT/70L [III LECTRODE lNl/EA/TOR J. R. PIERCE A TTOR/VE V July 4, 1950 R PIERCE 2,513,359

ELECTRON DISCHARGE DEVICE OF THE CAVITY RESONATOR TYPE Filed Feb. 1, 1945 2 Sheets-Sheet 2 5 -sa ii //V [/5 N TOR J. R. PIERCE A T TORNE V Patented July 4, 1950 ELECTRON DISCHARGE DEVICE OF THE CAVITYRESONATOR TYPE John R. Pierce, Millburn, N. J., assignor toBell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application February 1, 1945, Serial No. 575,587

1 Claim. (Cl. 315-5) This invention relates to electron discharge devices and, in one practical embodiment, to a reflex oscillator of the types disclosed in the applications Serial No. 575,584, filed Feb. 1, 1945, of S. O. Ekstrand and E. J. Walsh jointly and Serial No. 575,586, filed February 1, 1945, of F. H. Best.

The principal object of this invention is to provide a means for tuning a cavity resonator by change in its dimension which is exceedingly rapid, while at the same time; perhaps contrary to normal expectation, facile and sensitive, in operation. Additional, and more specific objects, will be evident from the following brief statement of the physical structure and attributes of the tuning system of the invention.

The invention makes use of thermal tuning and therefore to a distortion or dimensional change of the cavity resonator by the application of a stress, with a resultant strain, induced by thermal expansion. thermal tuner which is older in the art in which the heat, upon which the necessary expansion is predicated, is generated by a current flowing through the strain-producing element itself, or

through an operating means thereof, the heat .,.1

in the present invention is generated by electron bombardment of said strain-producing element or operating means therefor.

The invention, in an important aspect, is an improvement over that disclosed in W. G. Shepherd application, Serial No. 575,585 filed February 1, 1945, and a specific object of the invention to provide a more facile and sensitive, while at the same time more energetic, control over the generation of heat by electron bombardment than B is a'lfordedby the Shepherd invention. This object is achieved by the use of a third electrode (that is, in addition to the electron source and bombarded element) in the tuner unit, the potential on which with relation to the electron source determines the extent and velocity of electron flow from the cathode to the bombarded element.

A still further object is to provide a more simple functional relationship between the ther-' As distinguished from a:-

with reference to the accompanying drawing in which:

Fig. 1 discloses, partially diagrammatically and in section, and with a minimum necessary detail to teachthe principles of the invention, an illustrative embodiment of the invention; and,

1 Figs. 2, 3 and 4 illustrate in complete structural detail an embodiment of the invention which has proved effective in practice, Fig. ZcOmprising an elevational view mainly in section of such. em-

bodiment and Figs. 3 and 4 comprising respectively a'perspective view of the-thermal tuning unit assembly included in the Fig. 2 organization and a perspective view of the coupling between said tuner unit assembly and the cavity resonator, which also is a part of said organization, portions of the structure being broken vaway to show details thereof more clearly.

1 Figs. 2, 3 and 4 of the drawing are substantial duplicates, in fact'exact duplicates to all intents and'purposes of Figs. 1, 3 and 4 of the aboveidentified F. H. Best application, which is being filed currently therewith. Because of the use of the same reference characters in Figs. 2, 3 and 4 'of the present case as in Figs. 1, 3 and 4 of Best, a

new series of reference characters, beginning with numeral [ill will be used for Fig. 1, which is original in this application.

Referring now to- Fig. 1, the cavity resonator NH thereof is here shown exceedingly diagram-- matically as the frequency determining element of a reflex oscillator, this type of oscillator, which employs velocity variation in a particular way and which is principally characterized by the use of a single cavity resonator to perform the functions otherwise requiring the use'of at least two such resonators, is now well known in the art. The later numbered figures disclosed as above, a complete embodiment of such an oscillator. I This oscillator is completed as to its more essential elements in Fig. 1 by the electron gun shown generally at m and by repeller electrode H33. 'By the'electron gun, electrons are generated and impelled through imperforate boundary walls of said resonator toward the repeller electrode which repels or-r eflects them preferably without actual interception of any of them inthe process. The electrons then retrace their path through the resonator-to there impart energy to it so that such resonator can function analogously as the tuned circuit of a lower frequency oscillator. Energy may be abstracted therefrom by coaxial conductor-or the like I04. 1

- It isimportant to-note that the invention ha principally to do -with the movement of flexible 3 diaphragm 15 of said cavity resonator axially of it and therefore in the direction of electron flow so as to linearly vary its natural frequency responsive to said movement. It is therefore impartial as to the particular function of the resonator in the general organization so that the resonator could equally well be, for example, one of the cavity resonators of the so-called Klystron; disclosed in United States patent to Varian 2,242,275, May 20, 1941, or the cavity resonator of the related organization disclosed in Llewellyn 2,190,668, February 20, 1940. These organizations are cited only by way of examples and the principle of the invention is operative with respect to any cavity resonator whatever which is adapted by design for tuning in the manner required regardless of how said resonator is used in combination.

The diaphragm I is directly actuated by the extension or contraction of a thermally responsive element lllli which is rigidly fixed at its top to support I01. Because so rigidly fastened the change of length of element I06 is reflected altogether as a corresponding movement of the diaphragm. This drive means is distinguished by its simplicity and directness although, as exemplified in the more practical embodiment of "the later numbered figures, the design may eas- "ily be such as to provide the requisite degree of "linearity with other desirable qualities without attendant sacrifices of otherwise desirable prop- "erties because of this simplicity and directness.

Said thermally responsive drive element I06 responds to heat generated in the same by bombardment by electrons emanating from electron source I08, which therefore simulates in function and may well simulate in appearance the conventional cathode of electron discharge devices gen- -erally. The potential source I09 cooperates to this end, that is, to insure that electrons emanat- "ing from the cathode are attracted to the boml'barded element or anode. =ing efiect, as conditioned quantitatively by the electron bombardment, is a function of this cathode-anode potential, as in the related Shepherd 1 invention, the control here contemplated Y is achieved by the use of a third electrode I ll] which Although the heatexerts a controlling effect on the electron stream Although I I I is shown as providing a, means for varying the hence the tuning efiect eventually impressed on 4 I H19 which is common to the oscillator and control unit. The cathodes of the oscillator and control unit are connected as shown, so that the control electrode of the control unit has impressed on it a variable potential with respect to its cathode from said source III in conjunction with source Illa.) When connected in this way.

when the oscillator is slightly tuned, as it might be in practice, by change of repeller potential, the means of this invention would tend to conform the tuning of the cavity resonator to the including a cavity resonator, and a thermally sensitive element for tuning the resonator and forming a part of a thermionic tuner unit. The enclosing vessel comprises a cylindrical metallic body I0 having an inwardly extending annular flange l l', e, cup-shaped metallic base member l2 sealed, as by welding or brazing, to one end of the body I 0 and having therein a plurality of eyelets [3 to which leading-in conductors I4 are sealed hermetically by vitreous masses or beads 15, and a metallic, cup-shaped cap or closure I6 sealed, as by welding or brazing, to the other end of the body I0.

The reflex oscillator comprises a generally toroidal cavity resonator I! bounded by a metallic disc l8 having a flexible, annularly corrugated diaphragm portion l9, a second rigid metallic disc 20 having a central frusto-conoidal portion ZI' aligned with a central opening in the diaphragm portion I9 and a metallic spacer ring 22.

Opposite the frusto-conoidal portion 2! and axially aligned therewith is an electron gun which includes a cylindrical cathode member 23 having a concave end surface 24 coated with electron emissive material, a heater filament 25 with- ,inthe cathode membelya heat shield 26 encompassing the cathode member, and a cylindrical beam forming electrode 21. The beam forming electrode 21 and shield 25 are provided with juxtaposed flanges 23 and 29 respectively which are joined to each other and are held. between insulating discs 30 and Bi seated within a flanged quite analogous to that of the usual control e'lectrode of a thermionic triode device.

the control electrode H0 is outside of the oathode and anode, this relationship is not necessary although it would tend to be used for reasons 1 of convenience. Conventionalized variable source 155 a negative potential on this control electrode and disclosed among other things in the Shepherd application, the control may be automatic to determine an equality, or constant difierence, of frequency, with a standard wave. As used in a reflex oscillator the tuning unit could even be tor cathode or electron gun [02 on the repeller 1 03. The resonator has a positive potential with respect to said cathode impressed from source cup-shaped member 32. The cathode member 23 is afiixed at one end to the shield 26 and the latter is connected electrically to one of the leading-in conductors 33 for the heater filament 25 by a tie wire 34. The elements of the electron gun together with the discs l9 and 20, the spacer 22 and a second spacer ring 50 are locked to the flange II by a C-shaped washer or clamping member 35 and a plurality of screws 36, only one of which is shown, threaded into the flange II.

The frusto-conoidal member 2|, beam forming electrode 21 and cathode are so constructed and arranged, in ways known in the art, that elec trons emanating from the surface 24 are concentrated into a converging beam substantially focussed upon the gap between the smaller end of the member 2I and the portion of the diaphragm l9 opposite thereto.

Energy may be taken from the oscillating field within the resonator I! by way of a wave guide which may be of rectangulated cylindrical crosssection, and comprises an inner portion 31 af fixed to an eyelet 38 on the disc 20 adjacent a slot 86 in the ring 22, the portion 31 extending into immediate proximity to an aperture 39 in the base member I2, and an outer portion 48 affixed to the base member I2, in alignment with asrasse the-inner portion 31 and sealed hermetically atits outer end by a vitreous mass. 4| abutting a ceramic disc 42 fitted. within the portion ML.

The inner portion 31 of the wave guide has afifixed thereto a trough-shaped metallic annulus l3 which in turn mounts a metallic cylinder 44, the annulus 4:3. and cylinder 44: defining a choke joint with the juxtaposed portion of the base [2 to prevent loss of energy from the guide. 3:1,. 40.

Opposite the diaphragm I 9 and aligned wi the central; aperture therein is a tubular repeller. electrode 45. which is locked. in a. cylindrical ceramic body 46 fitted Within a cylindrical metallic sleeve 4'! and locked therein by a collar or band 85. The sleeve 41 is secured Within. a metalliccoupler element 48 having a tapered end D01.-

tion 49 secured tothe diaphragm. IS. The other end Of the coupler 48 has affixed thereto a rigid metallic disc 5| to the center of which a rigid metallic drive rod 52 is. secured. For reasons which will appear presently, the drive rod 52 is of a material, such as. stainless. steel, having. a high temperature coefficient of expansion and contraction. Extending through an insulating tubulature 53 carried by the disc 5| is a leading-in connector 54 for the repeller electrode 45.

The assembly comprising the coupler 48, 49' and repeller electrode 45 is supported for axial movement as. a unit by a pair of resilient spider members, the arms 55 of which, as shown in. Fig. 4, radiate from integral collars 56 aflixed to the coupler 48, to integral annuli 5T seated against opposite ends of a cylindrical spacer 58' fitted within the body It).

During operation of the device, electrons emanating from the cathode surface 24 are projected across the gap in the cavity resonator IT and are velocity varied due to the oscillating field within the resonator. The velocity varied electron stream issuing from the aperture in the diaphragm I9 is subjected to a retarding field'due to the repeller electrode 45, whereby the direction of motion of the electrons is reversed and the electrons are again projected into the resonator in the form of a density varied stream to deliver energy to the field within the resonator and thus to sustain oscillations. The oscillation frequency will be dependent, of course, upon the resonant frequency of the resonator and. the latter, in turn, is dependent upon the configuration of the cavity. The configuration and, hence, the resonant frequency, is adjustable by deflection of the diaphragm l9. As is apparent, displacement or deflection of the diaphragm may. be effected by longitudinal motion of the drive rod 52. Such motion of the rod 52 is realized and controlled accurately by varying the temperature of the rod to cause it to expand or contract to tune the cavity resonator-to the desired frequency. The control of the rod is effected by a thermionic unit, oi" which a portion of the rod constitutes the anode.

The thermionic tuning unit is fabricated as a unitary assembly which comprises, as shown clearly in Figs. 2 and 3, an annular foundation member or platform 59 provided with integral ears 6!) and a dished plate 6|, the member 59 and plate 6| being coupled together by rigid posts 62 abutting the plate BI and the ears 60. Supported in parallel relation by the posts 62 are a pair of insulating discs 63 and 64 which mount, in turn, a cathode and a control electrode cooperatively associated with the drive rod 52. The latter extends through oversized apertures in the discs GI, 63 and 64 and has its upper end secured to a rigid. bridge. defined. by a bracket I02 and a bent strap or lever 65: affixed to the disc 5|.

The cathode of the tuner unit comprises a cylindrical metallic tube 61 parallel to, the rod 52' and having a coating of electron emissive material upon. its. outer surface, and a folded heater filament 6131 Withinthe cathode tube 6.7. The control' electrode 5-9 is of rectangular form, encompasses the cathode 6.1 and rod 52 and is locked to the insulating discs; 53 and 64 by integral bentover tabs. 1 i.

In the fabricationof the device, after the tuner assembly has been mounted as described hereinaiter, the strip or lever 651s flexed to move the drive. rod 52' longitudinally, and thus to move the. coupler-repeller electrode assembly and displace the diaphragm It, to. tune the cavity resonator to a prescribed frequency. The end of this strip is then afiixed, as by welding, to the bracket 10. Thereafter, as will be apparent, the natural fre quency of the resonator will vary in. accordance with longitudinal. expansion and contraction of the drive rod 52,. one end of the rod being fixed against displacement by the bridge 65, 10. The length of this rod at any time will be dependent upon. the temperature thereof and the temperature, in turn, will be determined by the bombardment of the rod by electrons emanating from the cathode 67, the rod, as noted heretofore, serving as an, anode. The electron current to the rod is controllable by the control electrode 69. Thus, by adjusting the potential of the electrode 69-, the resonant frequency of the cavity resonator may be altered or maintained fixed despite variations in the configuration. of the cavity resonator due to. temperature effects. in the operation. of the device.

It is. evident. that extremely fine tuning of the cavity resonator is. attainable. Also, inasmuch as the repeller electrode 55. is coupled mechanically to the diaphragm l9 and moves therewith, the spacing of the repeller electrode relative to the diaphragm is fixed, whereby, for any given potentials upon the elements of the oscillator, the transit times for electrons leaving the cavity resonator and returning thereto. likewise are fixed. Further, because of the mounting of the coupler d8 by the spiders, displacement of the coupler isli-nearwhereby a predeterminable relation between resonator frequency and control electrode potential. is achieved.

Supported from the discs 63 and 64 by bent wires 12 locked to these discs are a pair of filaments 73* which are coated with a getter material and are connected electrically at one end by a fuse wire M. A protective shield 15, mounted upon two. of the posts 52, is interposed between the control electrode 59 and the getter coated filaments." During the evacuation treatment of the device, a suitable current is passed through the filaments "I3 by way of the leading-in conductors for two of the electrodes of the device, to flash the getter material". An increased current pulse is then applied to melt the fuse wire 14 and, thus, break the electrical connection between the two conductors mentioned.

mectrical connection between the leading-in conductors It and the electrodes of the oscillator and thermionic tuner unit may be established by way of conductors, for example wires 15 encased in insulating sleeves H, to which the conductors l4 and electrodes are connected by tie wires or strips 18. The specific connections may be varied, of course, and will be apparent without further description.

is brazed to the diaphragm l9. eration, the coupler 48 is centered accurately, as 1 by a suitable jig, with respect to the body l and thus, is aligned accurately with the diaphragm. In order to prevent damage to the diaphragm vice wherein all the parts are held securely in place and wherein the parts of the oscillator unit are aligned very accurately, for example coaxial within less than .001 inch. The general method of assembly and fabrication is, briefly, as follows:

The disc l8, I9 is brazed to the flange I l on the body' Ill. The spiders are secured to the coupler 48 by welding the collars 56 thereto and this assembly together with the spacer 58 is inserted into the body I0 and the spiders are brazed to the spacer 58, the latter is brazed to the body l0 and the smaller end of the frusto-co-nical portion 49 During this opduring subsequent operations, a lock member 80 having a slotted end 8l for accommodating the flange on the coupler 48 is secured to the spacer motion of the coupler and, hence, displacement 58, the slot bein of such width as to limit axial of the diaphragm, to, for example, of the order of a few thousandths of an inch.

A subassemblycomprisin the repeller electrode 45, insulator 46 and sleeve 41, constructed so that the repeller electrode is accurately coaxial with the outer surface of the sleeve 41, is

inserted within the coupler 48 until the electrode 45 rests upon the frusto-conical portion 49 and then is withdrawn a distance requisite to establish the prescribed spacing between the repeller electrode and the diaphragm l9, whereupon the sleeve 47 is welded to the coupler 48. Thus, the repeller electrode 45 is aligned coaxially with the f frusto-com'cal portion are aligned accurately while viewing with a microscope.

Another subassembly comprising the cathode" 23, 24 shield 25, insulators 30 and 3| and cupshaped member 32, but not the heater. 25, is then fabricated, aligned with the apertures in the portion 2| and diaphragm [9 while viewing with a microscope through the central aperture in the dished portion 24 of the cathode, and is then secured to the flange I by the screws 36.

The cap or closure 5| with the drive rod 52 fixed thereto, is affixed, as by welding, to the coupler member 48, a portion of the flange of the cap 5i being cut away, as shown in Fig. 4, to clear the slotted end portion BI of the lock member 80.

This portion is then bent away from the coupler member 48 and severed.

Subsequently, the thermionic tuner assembly is threaded over the rod 52 and the platform 59 is seated'upon the upper spider member (in Fig. 2) and locked in place by forcing a portion of the body I0 thereagainst as indicated at 82 in Fig. 2. The drive rod 52 then is welded to the bridge piece and the latter is flexed to tune the cavity resonator and welded to the bracket 10, as noted heretofore.

It is to be noted particularly that the construction above described enables very exact coaxial alignment of theelements of the oscillator whereby predeterminable and stable operating characteristics are obtained. Further, it will be noted that in'the completed device the internal elements are mounted securely in fixed relation whereby the device may be subjected to relatively strong shocks without disturbance of the desired space relation of the parts.

Although a specific embodiment of the invention has been shown and described, it will be understood that it is but illustrative and that various modifications may be made therein without departing from the scope and spirit of this invention as defined in the appended claim.

What is claimed is:

' An electron discharge device comprising, a frequency-significant mechanical-electrical network including a frequency determining movable element, means cooperating with said network comprising an electron discharge device constituting, with said network, an oscillation generatin circuit whose characteristic frequency is the natural frequency of said frequency-significant circuit, and afreq'uency adjusting assembly comprising the anode of said electron discharge device, which has an elongated form and whose longitudinal axis extends in parallel with the desired direction of movement of said movable element and which is directly connected thereto, and having a high temperature coefficient of expansion and contraction whereby its length varies in accordance with its contained heat, the oathode of said electron discharge device, which is in electron bombarding relation to said anode, and a control electrode positioned in operative relation to said electrons and whose potential with respect to said cathode therefore determines the condition of the electron bombardment, and hence the heat condition, of said anode.

JOHN R. PIERCE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,419,547 Ehret June 13, 1922 1,565,151 Houskeeper Dec. 8, 1925 1,740,202 Riiben Dec. 1'7, 1929 2,374,810 Fremlin May 1, 1945 2,408,817 Snow Oct. 8, 1946 2,414,785 Harrison et al Jan. 21, 1947 2,438,132 Snow Mar. 23, 1948 2,454,306 Clifford et a1 Nov. 23, 1948 

